As i understand it is advisable to "bake" cast iron prior spraying for the oils to burn out. What temperature and duration should be enough for this ?

After that i am planing on grit blasting, wire flame spray NiAl, and wire flame spray Metcoloy 2 to thickness of ~4mm. As there is no corrosion i wont be using sealer.
Machining to ~3-3.5mm thickness is next. Maybe you would have any additional suggestions or insights for this kind of job ?

We find that if we 'thermal degrease' at 400 centigrade
we have good success. As a general rule we allow the usual one hour for each inch of material thickness. The rest of your planned procedure seems OK.